If you've been to the ophthalmologist and your vision for each eye is 20/20 and the visual field is within DMV standards, maybe you should try consulting a neuro-ophthalmologist. (If you're currently in the Charlotte area Dr. Waller at Horizon Eye is a pretty good.)
I believe Dr Grayson at genesis eye center in Charlotte NC did check me for a visual field test. After this, I went ahead and tried the vision test at the DMV. I had the same problem again - I could not see the middle column. So I read the first column, closed one eye and middle column appears, read it (during this time, one of the other columns disappears), opened both eyes and read the third column and passed the test. I moved to IL near Chicago and had to do take the vision test up again last year at the DMV, I had the same thing happen to me all over again. I passed the test the same way.
Are there any other vision tests (apart from a second opinion) that I could take to find out why I am not able to see all the letters on all 3 columns of a DMV vision test?
Usually amblyopia would show some definite degree of vision, so if your vision was perfect that would generally rule out amblyopia. I suggest you have a visual field test as well as a complete eye exam with a board-certified ophthalmologist. I don't know what else to tell you other than perhaps you need a second opinion. Amblyopia would be one of several conditions that could make you fail a DMV test.
MJK MD